The invention relates to electrical bushing assemblies.
A known bushing assembly includes an elongated contact and an insulating shank molded around the contact. The shank includes integral flanges or ears which can be fastened to the tank of an electrical apparatus, such as an oil insulated transformer. Each flange or ear has therethrough an aperture, and the tank includes mounting studs extending through the apertures. Nuts are threaded onto the mounting studs to secure the bushing to the tank. A portion of the shank and the contact extend through a bore in the tank wall, and an annular gasket surrounds the shank portion between the bushing and the tank wall to seal the joint therebetween.
In some known bushing assemblies, the gasket is located in a complementary recess in the bushing, with the gasket completely filling the recess when the gasket is uncompressed. As the bushing is secured to the tank and the gasket is compressed, the gasket acts like a hydraulic fluid, concentrating stress on the molded insulating shank of the bushing. If this stress exceeds the material strength of the shank, the shank breaks.
A typical tank wall is not completely flat. Furthermore, the tank wall can bulge when the oil inside is heated by transformer losses, or can buckle as the oil cools. If the nuts are tightened down so that the ears are tightly mated with the tank wall, a change in the shape of the tank wall can fracture the bushing ears.